In a power supply device using a Scott connected transformer made of a main transformer and a teaser transformer, it is considered to provide control elements to control a voltage or a current in each of three phases of the Scott connected transformer on the primary side in order to control an output voltage of the main transformer and an output voltage of the teaser transformer.
Because a current flowing through a primary coil of the teaser transformer also flows into a primary coil of the main transformer, even with the arrangement of control elements in three phases of the Scott connected transformer on the primary side, individual control of output voltages in two single-phase circuits is not possible.
Due to the above reason, a general method is to control output voltages in two single-phase circuits individually by providing a control element in each of two single-phase circuits respectively in order to control a voltage and/or a current therein.
However, if a load connected to a single-phase circuit has low resistance, the single-phase circuit becomes a large current circuit where arrangement of control circuit is difficult practically. Therefore, a configuration as shown in FIG. 13 is adopted where control elements are arranged in two single-phase circuits that are made of Scott connected transformers and two sets of single-phase transformers are further arranged to transform outputs of the two single-phase circuits to low-voltage large currents. That is, this method requires a total of three sets of transformers including one set of Scott connected transformers and two sets of single-phase transformers.